Here's the most worrying sign from the latest report on Russia's recession

Capital Economics Russia's economy saw a big contraction in 2015, though the silver lining is that the data was better-than-expected.

However, analysts at Capital Economics caution that there's also something alarming about the data: there was a slowdown in December.

Preliminary GDP data showed that the Russian economy shrank 3.7% in 2015, less than expectations for a 3.8% drop.

Additionally, analysts estimate that the economy contracted by 3.5% year-over-year in Q4, shallower than the 4.1% fall in output in Q3.

All of this sounds pretty good at first.

But as Capital Economics' senior emerging markets economist William Jackson writes, "Worryingly, December's activity data ... suggest that the economy deteriorated towards the end of the fourth quarter." This means things are likely to get worse before any meaningful turnaround.

Jackson points to three key data points that saw ugly drops in particular:

Industrial production plunged 4.5% y/y in December, following a 3.5% contraction y/y in November.

Fixed investment fell 8.7% y/y, following a drop of 4.9% y/y in November.

Jackson also notes that the "unfavorable base effects" in Russia's economy alone don't seem to account for this significantly weaker data than analysts were expecting.

It's also worth noting that Russia's late Q4 weakness coincided with December's decline in oil prices.

Prices fell even lower in January, with Brent trading near $31.30 per barrel today, less than $37.60 per barrel at the end of December.

And while it's too simplistic to equate low oil prices with a weak Russian economy, Capital Economics' Neil Shearing and Liza Ermolenko argued last week that "it's clear that Russia is worse off when oil prices fall."

"In short, the data highlight that while the worst of Russia's crisis has now passed, the economy is still extremely weak. The latest fall in oil prices and drop in the ruble mean the likelihood of a second consecutive year of recession are rising," concludes Jackson.